Method for scintillation counting

ABSTRACT

A METHOD IS PROVIDED FOR COUNTING ATOMIC DISINTEGRATIONS OF RADIOACTIVE MATERIAL WHICH IS ACCOMPANIED BY EMISSION OF B-RAYS, WHEREIN THE MATERIAL IS DISPERSED IN A SCINTILLATION LIQUID WHICH CONTAINS AN OXDIAZOLE COMPOUND OF THE FORMULA   A1-1,4-PHENYLENE-(1,3,4-OXADIAZOL-2,5-YLENE)M-   1,4-PHENYLENE-B1   WHEREIN A1 IS A BRANCHED CHAIN ALKYL, B1 IS HYDROGEN, PHENYL, LOWER ALKYL, OR LOWER ALKOXY, AND M IS 1 OR 2. THE COUNTS PER MINUTE EMITTED BY THE MATERIAL DISPERSED IN THE SCINTILLATION LIQUID ARE MEASURED WITH A SUITABLE INSTRUMENT SUCH AS LIQUID SCINTILLATION SPECTROMETER.

United States Patent 3,650,973 METHOD FOR SCINTILLATION COUNTING Erwin Maeder, Aesch, Basel-Land, Rudolf Anliker, Binningen, Karl Schmid, Reinach, Basel-Land, and Adolf Emil Siegrist, Basel, Switzerland, assignors to Ciba Limited, Basel, Switzerland N0 Drawing. Continuation of application Ser. No. 577,168, Sept. 6, 1966. This application July 31, 1969, Ser. No. 850,312 Claims priority, application Switzerland, Sept. 15, 1965, 12,815/65 Int. Cl. C09k 1/02 US. Cl. 252-301.2 6 Claims ABSTRACT OF THE DISCLOSURE A method is provided for counting atomic disintegrations of radioactive material which is accompanied by emission of B-rays, wherein the material is dispersed in a scintillation liquid which contains an oxdiazole compound of the formula \ClQe Llt td. wherein A is a branched chain alkyl, B is hydrogen, phenyl, lower alkyl, or lower alkoxy, and m is 1 or 2. The counts per minute emitted by the material dispersed in the scintillation liquid are measured with a suitable instrument such as a liquid scintillation spectrometer.

This application is a continuation of Ser. No. 577,168 filed Sept. 6, 1966, and now abandoned.

The present invention relates to the use of selected oxdiazole derivatives for scintillation counting methods in atomic disintegrations.

While a number of oxdiazole derivatives have already been proposed for use in scintillation counting, especially in liquid systems, these compounds do not satisfy fully all the requirements they should satisfy. This refers above all to a high energy transfer at an extremely short extinction time combined with a low absorption coeflicient for self-quenching and with a high solubility in the solvents or solvent systems preferably employed in liquid scintillation counting methods. An adequate chemical stability (stability towards the action of light and towards acids and alkalies) is moreover a precondition for their suitability anyway.

It has now been found that a small selection of certain oxdiazole derivatives satisfy all of these requirements. According to this invention there are thus used oxdiazole derivatives comprising the structural element Q i A1 C C LIL-1U. in which A represents an alkyl group which contains 3 to 7 carbon atoms and at least one chain branching, and

B represents a hydrogen atom, a phenyl group, an alkyl group having 1 to 7 carbon atoms, which may be branched,

3,650,973 Patented Mar. 21, 1972 or a lower alkoxy group, and m1=1 or 2 as scintillation substance for use in liquid scintillation counting.

The scintillation liquids concerned are characterized in that they contain as solvent benzene or an alkylbenzene which is liquid at room temperature or a dioxane-l-naphthalene-l-water mixture and 0.01 to 5% by weight (referred to the total weight of thescintillation liquid) of an oxdiazole derivative of the Formula 2.

Of special importance within the scope of this invention is the use of oxdiazole derivatives of the formula 11,5 ILA in which B represents a tertiary butyl group or a phenyl group-in liquid scintillation counting methods. In this case the scintillation liquids contain preferably toluene as solvent and 0.01 to 5% by weight (referred to the total weight of the scintillation liquid) of an oxdiazole derivative of the Formula 3.

As examples from the above-mentioned types of oxdiazoles the following compounds may be mentioned:

From the foregoing it will be realized that the use of the said scintillation substances is of special importance to liquid scintillation counting methods in conjunction with certain solvent systems. Thus, this invention further includes a method of counting atomic disintegrations ac companied by the emission of fl-rays, by means of the liquid scintillation method in predominantly aromatic hydrocarbons as scintillator solvents, characterized in that the scintillation liquid used is a solution of an oxidazole of the formula to say as a primary substance activated to emit light by an energy-rich radiation released by an atomic disintegration; these primary substances are combined with the usual secondary solutes, that is to say substances distinguished by an emission of longer wavelength. Such suitable secondary solutes are, for example, 1,4-di-[2-(5- phenyloxazolyl)] benzene, 1,4 di [2-(4-methyl-5- phenyloxazolyl)] benzene and 1,4 di (4-isopropylstyryl)-benzenes. Furthermore, they may be combined with neutron capture solutes, gamma conversion solutes, further solvent additives, gels, suspending assistants or solubilizers. The counting method used may, of course, be either an internal or an external method.

Suitable solvents for the liquid scintillation counting method are above all aromatic hydrocarbons that are liquid at room temperature (provided no solvent combination is used) such, for example, as benzene, toluene, a xylene, ethylbenzene, 1,3,5-triethylbenzene, cumene, a cymene, phenylcyclohexane, also ethers such as anisole, dioxane, 1,2-dimethoxyethane; non-aromatic hydrocarbons such as cyclohexane, heptane and the like; or finally solvent mixtures such as toluenef+methanol and possibly water, toluene-i-ethanol, naphthalene+dioxane, naphthalene-l-toluene and possibly water, naphthalenej-l-dioxane +water, 2-methoxyethanol-l-naphthalene+toluene and possibly water, naphthalene+tributylphosphate or other commercial mixtures of aromatic hydrocarbons recommended for these purposes.

The concentration of the oxdiazole derivatives to be used in the present process may principally vary within wide limits which are defined or restricted by practical considerations. For example in the lower region it must be chosen so that an adequate transmission to the photomultiplier is ensured, whereas the upper region is delineated by the appearance of visible absorption of the selfquenching. Though thus, for example, for the preparation of stock solutions (which are suitably diluted for use) concentrations of 10% or higher are quite acceptable, the working concentrations most suitable for actual practice range approximately from 0.1 to 3%, preferably from 0.4 to 2% (all percentages are by weight, referred to the total weight of the solution).

Apart from toluene, preferred solvent systems are the systems toluene+methanl 1:1) with the addition of about 2% of water, 2-methoxyethanol+toluene+naphthalene (40:60:8) with addition of up to 4% of water, dioxane+toluend+naphthalene (40z 60z8) with up to of water, or toluene-1-methanol-l-ethanolamine (50:44:6). The composition of the solvent system depends above all on the nature of the substrate or of the isotope to be counted. For isotope counting there are, for example, most frequently used C H S P Fe Fe 1125 d 1131- The technical advance residing in the oxdiazoles to be used in this invention is especially the fact that they represent as such scintillators that can be used by themselves (that is to say without a secondary solute) which not only satisfy all other requirements to a great extent but above all also display excellent solubility properties such as the hitherto known highest grade scintillators of the oxdiazole series did not possess. This is especially true of the particularly good solubility in transparent solvents having a high flash point.

In addition to the range of applicability described above the oxdiazoles defined above may be used quite generally wherever the task involved is the transformation of an energy-rich radiation into measurable light.

An important sphere of application is, for example, their use for so-called plastics scintillators. In this use the scintillator may be homogeneously dispersed in the polymers concerned (polymerizate, polycondensate or polyadduct) before proceeding to the final shaping operation (casting, drawing, moulding, injection moulding or the like), and the whole is then shaped. According to another possibility the scintillator is added to the starting materials (10) iii-@430 OH or of an ester thereof with 1 mol of hydrazine in the presence of a phosphoric acid whose water content is inferior to that of orthophosphoric acid (especially polyphosphoric acid); this method is particularly suitable for synthesizing symmetrical oxdiazoles, that is to say those in which A =B or (b) By treating a diacylhydrazine of the formula (for m=1 according to Formula 2) with a non-sulphonating dehydrating agent, or

(0) By reacting an imidoether upon a suitable carboxylic acid hydrazide at an elevated temperature in the presence of a solvent.

Unless otherwise indicated, parts and percentages in the following manufacturing instructions and examples are by weight.

(A) 10.0 parts of hydrazine hydrate are stirred dropwise at 50 C. into 400 parts of polyphosphoric acid (83 P 0 with the temperature rising to about C. Then 71.2 parts of para-tertiary butylbenzoic acid are added and while excluding air the temperature is raised within 30 minutes to C. The batch is stirred for 8 hours at 125 to C., whereupon a clear colourless solution forms. After cooling to about 50 C., the whole is vigorously stirred into 1000 parts of cold water, the precipitated reaction product is suctioned off and washed with water until the washings run neutral to Congo red. After drying, there are obtained 66.7 parts (=100% of theory) of 2,5-bis-[4'-para-tertiary butylphenyl-(1)]-l,3, 4-oxdiazole of the formula forms colourless flakes melting at 139 to 141 C.

(B) 29.6 parts of the diacylhydrazine of the formula are brought to the boil in parts by volume of freshly distilled thionylchloride within one hour while being stirred, and the whole is then refluxed for 2 hours, whereupon a clear, pale-yellow solution forms. The excess thionylchloride is then distilled off, first under atmospheric pressure and then under vacuum. The residue is triturated with ice water, whereupon it solidifies; it is filtered off, washed with water until the washings run neutral and dried, to yield about 27.6 parts =99.3% of theory) of 2- [4'-tertiary butylphenyl-(l') ]-5-phenyl-1,3,4-oxdiazole of the Formula 6 as a colourless powder which on recrystallization from ethanol+water (3:1) forms colourless flakes; it melts at 98 to 99 C. and displays in an ethanolic solution 3 absorption maxima at 288 m (e=30,400), 238 m (e=7550) and 232 111,41. (e=7350). Solubility in 100 ml. of ethanol at 20 C.: 4.00 grams.

The following 1,3,4-oxdiazole derivatives are accessible by the method described above:

a) 2- [4'-tertiary butylphenyl-l ]-5- [4"-methylphenyl-(1")]-1,3,4-oxdiazole of the formula Qr H323 NN in colourless, fine crystals from ethanol-l-water (7:2). Melting point: 111 to 112 C. Solubility in 100 ml. of ethanol at 20 C.: 2.92 grams. Ultraviolet absorption in ethanol, maxima at 291 mu (e=31,000) and 242 m (e=8650).

(b) 2-[4-tertiary butylphenyl-1')] [4" methoxypheny1-(1")]-1,3,4-oxdiazole of the formula mciz-Qt/ c-oom at; 1l 1l Colourless, fine crystals from ethanol, melting at 162.5 to 163.5 C. Solubility in 100 ml. of ethanol at 20 C.: 0.605 gram. Ultraviolet absorption in ethanol, A 298 m (e=32,000) and 249 m (e=6,100).

(c) 2,5-bis-[4-tertiary butylphenyl-(1)] 1,3,4 oxdiazole of the \Formula 5 [see above] (C) A mixture of 212 g. of diphenyl-4-car boxylic acid hydrazide and 2 liters of anhydrous ortho-dichlorobenzene is stirred at room temperature, then 197 g. of 4tertiary butylbenzoylchloride and 81 ml. of anhydrous pyridine are added; the thick paste is heated within one hour to 100 to 105 C. and stirred at this temperature for one hour. Within a further hour the reaction mixture is then heated to 140 to 145 C., whereupon an almost complete solution is obtained. 90 m1. of thionylchloride are then dropped in within 45 minutes at 140* to 145 C., whereupon a turbid solution forms which is stirred on for 15 minutes after the dropwise addition is complete.

The bulk of the solvent is then evaporated under vacuum and 1 litre of ethanol is dropped in so that the reac tion mixture is kept at the reflux temperature, whereupon a crystalline precipitate soon forms which is suctioned off at room temperature, and the filter cake is washed with alcohol and dried, to yield 295 g. of a greyis'h, crystalline powder melting at 135 to 136 C.

Crystallization from n-propanol with the aid of active carbon furnishes 240 g. of the compound of the formula EA; ILL-ll in the form of colourless prisms melting at 136 to 137 C.

C H ON (mol. weight: 354.43).Calcula-ted (percent): C, 81.32; H, 6.26; N, 7.90. Found (percent): C, 81.27; H, 6.14; N, 7.92.

(D) 5.2 grams of oxalic acid dihydrazide and 10 ml. of anhydrous pyridine are added at 40 to 50 C. to a solution of 14.5 g. of 4-isopropylbenzoylchloride in 20 0 ml. of anhydrous ortho-dichlorobenzene. In the course of 2 hours the reaction mixture is heated to 130 to 135 C., whereupon a thinly liquid paste is obtained. Within 30 minutes at 130 to 135 C. 20 ml. of thionylchloride are dropped in, whereupon a clear solution forms which is stirred for another minutes at this temperature and then allowed to cool.

The excess thionyl chloride and the solvent are then almost completely evaporated under vacuum. The residue is stirred with 100 ml. of methanol, whereupon a lightbrown, crystalline precipitate is obtained which is suctioned off and washed with methanol.

Two recrystallizations from alcohol in the presence of bleaching earth furnish 7 g. of the bis-oxdiazoyl compound of the formula 6 in the form of small colourless needles melting at 175 to 176 C. C H 0 N (mol. weight: 374.45).Calculated (percent): C, 70.57; H, 5.92; N, 14.96. Found (percent): C, 70.65; H, 5.91; N, 14.84.

In the following examples all measurements were recorded in counter tubes poor in potassium with the use of a liquid scintillation spectrometer Tri-Carb model -Ex-2, makers Packard Instrument Co., Inc., Illinois.

EXAMPLE 1 20 ml. each of a solution of 5 g. of the compound of the Formula 9 and of the Formula 5 in 1 litre of toluene are introduced into a counter tube and mixed with 1 ml. of a solution of benzoic acid marked with C having an activity of 0.01 microcurie. The counter tube is inserted into the counter and the counts per minute =:c.p.m.) are counted. At a high-woltage of 900 volts and a calibration from 100 to 600 there are recorded 13,630 c.p.m. for compound 9 and 13,200 for compound 5.

EXAMPLE 2 20 ml. of a solution of 5 g. of the compound of the Formula 9 and of the Formula 5 in 1 litre of toluene are introduced into a counter tube, and 0.1 ml. of toluene marked with H having an activity of 0.01 microcurie, is added. At a high-voltage of 1100 volts and a calibration from 100 to 600 there are recorded 6600 c.p.m. for the compound 9 and 5930 c.p.m. for the compound 5.

EXAMPLE 3 20 ml. each of a solution of 10 g. of the compound of the Formula 9 and of the Formula 5 in 1 litre of toluene are mixed in a counter tube with 1.0 ml. of an ethanolic solution of 1-butyl-3-(para-tolylsulphonyl)-urea marked with The activity added is 0.01 microcurie. The counter tube is then inserted in the counter and the counts per minute are counted. At a high-(voltage of 900 volts and a calibration from 100 to 600 in the measuring channel there are recorded 13,200 c.p.m. for compound 9 and 12,950 c.p.m. for compound 5 EXAMPLE 4 20 ml. of a solution of 10 g. of the compound of the Formula 9 in a mixture of 400 ml. of methyl-Cellosolve, g. of naphthalene and 600 m1. of toluene are introduced in a small measuring cylinder, and 0.5 m1. of water marked with H having an activity of 0.01 microcurie, is added. At a high-voltage of 1200 volts and a calibration from to 600, 2200 counts per minute are counted.

EXAMPLE 5 A mixture of 1 g. of 2-[4'-tertiary butylphenyl-'(1')]- S-biphenylyl-l,3,4-oxdiazole of the Formula 9 and 100 g. of vinyltoluene distilled twice under 11 mm. Hg pressure (mixture of the ortho, meta and para isomers) is introduced into a Pyrex glass tube of 25 mm. diameter which is fused at one end. The tube is repeatedly evacuated to a pressure of 0.1 mm. Hg and scavenged with pure nitrogen. Finally, the tube is once more evacuated to 0.1 mm. Hg pressure and the tube is fused at the other end. The tube is then heated within 2 hours in a furnace to C. while ensuring by carefully revolving it that the compound of the Formula 9 is completely dissolved. To polymerize the batch in the tube it is maintained for 24 hours at 110 C., then heated for 24 hours at C. and for 48 hours at C. The following cooling and detensioning phase at 75 C. takes 81 hours. When the batch has cooled to room temperature, the resulting transparent polymer coreis recovered by smashing the glass tube. To measure the relative count rate the core is turned down to a diameter of 20 mm., sawn up into discs 10 mm. thick, and these discs are polished. The measure of the light output is the relative amplitude (RPH) of the counts produced by the Cs conversion electrons. For counting a. Philips 5 6 AVP photomultiplier with a ratio 2,2-paraphenylene-bis-(S-phenyloxazole):terphenyl of 1.30 (photomultiplier characteristic) is used. The counting standard used is the commercial plastics scintillator NE 102 A (makers Nuclear Enterprises Ltd.) whose RPH value is taken as equal to 1.00. The plastics scintillator according to this invention displays an RPH value of 1.10. A plastics scintillator prepared in identical manner from polyvinyltoluene, which contains 2% of the compound of the Formula 9 and 0.1% of 2- [4-biphenylyl-( 1') ]-6-phenyl-benzoxazole, gives the high RPH value of 1.23.

What is claimed is:

1. A method of counting atomic disintegration of a radioactive material which is accompanied by an emission of fl-rays, by means of the scintillation counting method which comprises dispersing said material in a scintillation liquid containing from about 0.01% by by weight of an oxdiazole of the formula in which A is an alkyl group which contains 3 to 7 carbon atoms and at least one chain branching; B represents a member selected from the group consisting of a hydrogen atom, a phenyl group, an alkyl group which contains 1 to 7 carbon atoms and a lower alkoxy group, and m is a whole number from 1 to 2, said oxdiazole being dissolved in a solvent selected from the group consisting of benzene, an alkylbenzene that is liquid at room temperature, a methanol+toluene-mixture, a Z-methoxyethanol-i-naphthalene+tolulene mixture and a di0xane+naphthalene-l-water-mixture.

2. A method according to claim 1 wherein said oxdiazole is 2-[4-tertiary butylphenyl-(1)]-5-phenylyl-l,3,4- oxdiazole.

3. A method according to claim 1 wherein said oxdiazole is 5,5-di[4-isopropyl phenyl-(1')]-2,2'-bi-1,3,4- oxdiazole.

4. A method according to claim 1 wherein said oxdi- UNITED STATES PATENTS 3,314,894 4/1967 Emery Nylas et al. 252301.2 3,244,637 4/1966 Kwan et al 252-3012 3,170,884 2/=1965 Macklin et al 252301.3 3,068,178 12/ 1962 Kallmann et al. 252-301.2

FOREIGN PATENTS 890,461 2/ 1962 Great Britain 260-307] 383,985 l/l965 Switzerland 260307.7 1,094,753 12/ 1960 Germany 260307.7

OTHER REFERENCES Hayes, I. N., Packard Technical Bulletin, No. 1 (revised January 1962), pp. 1-8.

Ott et al., Liquid Scintillators, XI I Absorption and Fluorescence Spectra of 2,5-Diaryl-1,3,4 Oxadiazoles, received May 24, 1960 in Patent Office.

'1. N. Hayes, D. G. Ott, and V. N. Kerr, Nucleonics, 13, No.12, 38 (1955).

JAMES E. POER, Primary Examiner W. T. SCOTT, Assistant Examiner US. Cl. X. R. 25071.5 

